U.S. patent number 6,001,152 [Application Number 08/865,622] was granted by the patent office on 1999-12-14 for flue gas conditioning for the removal of particulates, hazardous substances, no.sub.x, and so.sub.x.
Invention is credited to Rabindra K. Sinha.
United States Patent |
6,001,152 |
Sinha |
December 14, 1999 |
Flue gas conditioning for the removal of particulates, hazardous
substances, NO.sub.x, and SO.sub.x
Abstract
The present invention provides compositions including a salt
selected from the group consisting essentially of sodium nitrate,
sodium nitrite, ammonium nitrate, lithium nitrate, barium nitrate,
cerium nitrate, and mixtures thereof, as flue gas conditioning
formulations for use in controlling particulates, hazardous
substances, NO.sub.x, and SO.sub.x. For the purpose of obtaining
greater yields of particulate and hazardous substance removal, the
compositions may further include a polyhydroxy compound, preferably
selected from the group consisting essentially of sucrose,
fructose, glucose, glycerol, and mixtures thereof. Methods are also
provided for adding these compositions to the flue gas stream to
control particulate, hazardous substance, NO.sub.x, and SO.sub.x
emissions.
Inventors: |
Sinha; Rabindra K. (Moon
Township, PA) |
Family
ID: |
25345904 |
Appl.
No.: |
08/865,622 |
Filed: |
May 29, 1997 |
Current U.S.
Class: |
95/58; 110/216;
110/345; 423/239.1; 423/244.01; 95/129; 95/137; 95/71; 95/92;
96/108; 96/52; 96/74 |
Current CPC
Class: |
B01D
53/508 (20130101); B03C 3/013 (20130101); B01D
53/565 (20130101) |
Current International
Class: |
B01D
53/50 (20060101); B01D 53/56 (20060101); B03C
3/00 (20060101); B03C 3/013 (20060101); B03C
003/013 () |
Field of
Search: |
;95/58,71,72,92,128,129,135,137 ;96/27,52,53,74,108
;423/213.5,239.1,244.01 ;502/330 ;110/216,345 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
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Ceramic Society, 1964, vol. 1, pp. 322-339. Ref. QD 501.P3835.
.
Wendt, J. Q. J. et al., Effect of Ammonia in Gaseous Fuels On
Nitrogen Oxide Emissions, Journal of the Air Pollution Control
Association, vol. 24, No. 11 (Nov. 1974), pp. 1055-1058. .
Teixeira, D. P., The Proceedings of the NOx Control Technology
Seminar, Special Report No. EPRI SR-39, California, Electric Power
Research Institute, Feb. 1976. Reproduced by U.S. Dep't of
Commerce, National Technical Information Service PB-253 661. .
Minton, P.E. et al., "Heat Exchange Technology (Nonwater Media)."
in: Encyclopedia of Chemical Technology (3d ed.), vol. 12, pp.
171-191. Ref. TP9.E685 1978. .
Elliott, M. A., "Control of Pollution from Combustion Processes
(Sulfur Oxides)." in: Chemistry of Coal Utilization (New York, John
Wiley & Sons, 1981), 2d supp. vol., pp. 1462-1490. Ref.
TP953.N3 (1981 supp.). .
O'Sullivan, D., Method Uses Urea To Rid Flue Gas of NOx, Chemical
& Engineering News, (Apr. 18, 1988) p. 22. .
Markussen, J. M. et al., Performance of Soda Ash-Lime Sorbents in
Small-Scale Spray Dryer. Air & Waste Management Association,
Jun. 1989, Report No. 89-19.2, presented at 82nd annual meeting
& exhibition in Anaheim, California. .
Frank, N. W. et al., The Use of Electrons for Removal of SO.sub.2
and NOx Fom Flue Gases. Air & Waste Management Association,
Jun. 1989, Report No. 89-19.3, presented at 82nd annual meeting
& exhibition in Anaheim, California. .
Landreth, R. R. et al., Retrofit of Sorbent Injection Technology on
an Older Coal Fired Boiler. Air & Waste Management Association,
Jun. 1989, Report No. 89-19.4, presented at 82nd annual meeting
& exhibition in Anaheim, California. .
Pease, R. R. et al., Industrial Boilers: Status of Oxides of
Nitrogen Regulations and Control Technology in the South Coast Air
Quality Management District. Air & Waste Management
Association, Jun. 1989, Report No. 89-19.5, presented at 82nd
annual meeting & exhibition in Anaheim, California. .
Brinkmann, P. E. et al., NOx Emission Reduction From Gas Fired
Steam Generators. Air & Waste Management Association, Jun.
1989, Report No. 89-19.6, presented at 82nd annual meeting &
exhibition in Anaheim, California. .
Davis, M. L. et al., Choosing a Technology for Simultaneous Control
of NOx/SOx From Industrial Boilers. Air & Waste Management
Association, Jun. 1989, Report No. 89-19.8, presented at 82nd
annual meeting & exhibition in Anaheim, California. .
Grisso, J. R. et al., Operating Experience With SCR for NOx
Emission Control, ASME Industrial Power Conference, Oct. 1990,
presented in St. Louis, Missouri. .
Epperly, W. R., The World of NOx Reduction Chemicals. Chemtech
(Jul. 1991), pp. 429-431. .
Campbell, L.M. et al., Source book: NOx Control Technology Data.
North Carolina, Jul. 1991. Air & Energy Engineering Research
Laboratory, EPA-600/2-91-029, Reproduced by U.S. Dep't of Commerce,
National Technical Information Service PB91-217364. .
Makansi, J., Reducing NOx Emission From Today's Powerplants. Power
(May 1993), special report, pp. 11-28. .
Prasad, A., Air Pollution Control Technologies for Nitrogen Oxides.
The National Environmental Journal (May/Jun. 1995) pp.
46-50..
|
Primary Examiner: Chiesa; Richard L.
Attorney, Agent or Firm: Jones, Day, Reavis & Pogue
Claims
What is claimed is:
1. A compostion for use with an emission control device to remove
particulates and hazardous substances from a flue gas stream, said
composition located at a point upstream of said emission control
device and comprising a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, and mixtures thereof, provided that the
composition does not comprise ammonium nitrate and sodium nitrite
at the same time.
2. The composition according to claim 1, wherein the composition
comprises about 5% to about 25% sodium nitrate, 0% to about 25%
sodium nitrite, 0% to about 50% ammonium nitrate, and 0% to about
10% lithium nitrate.
3. The composition according to claim 2, wherein the composition
comprises about 8% to about 20% sodium nitrate, 0% to about 20%
sodium nitrite, 0% to about 44% ammonium nitrate, and 0% to about
6% lithium nitrate.
4. The composition according to claim 3, wherein the composition
comprises about 11% to about 15% sodium nitrate, 0% to about 15%
sodium nitrite, 0% to about 38% ammonium nitrate, and 0% to about
2% lithium nitrate.
5. The composition according to claim 1, further comprising a
polyhydroxy compound.
6. The composition according to claim 5, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
7. The composition according to claim 6, wherein the composition
comprises about 3% to about 26% of the polyhydroxy compound.
8. The composition according to claim 7, wherein the composition
comprises about 5% to about 20% of the polyhydroxy compound.
9. The composition according to claim 8, wherein the composition
comprises about 7% to about 14% of the polyhydroxy compound.
10. A composition for use with an emission control device to
simultaneously remove particulates, hazardous substances, and
NO.sub.x from a flue gas stream, said composition located at a
point upstream of said emission control device and comprising
cerium nitrate and a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, and mixtures thereof, provided that the
composition does not comprise ammonium nitrate and sodium nitrite
at the same time and further provided that the composition consists
of a dry powder when sodium nitrite is present.
11. The composition according to claim 10, wherein the composition
comprises about 5% to about 25% sodium nitrate, 0% to about 25%
sodium nitrite, 0% to about 50% ammonium nitrate, 0% to about 10%
lithium nitrate, and about 0.5% to about 10% cerium nitrate.
12. The composition according to claim 11, wherein the composition
comprises about 8% to about 20% sodium nitrate, 0% to about 20%
sodium nitrite, 0% to about 44% ammonium nitrate, 0% to about 6%
lithium nitrate, and about 1% to about 7% cerium nitrate.
13. The composition according to claim 12, wherein the composition
comprises about 11% to about 15% sodium nitrate, 0% to about 15%
sodium nitrite, 0% to about 38% ammonium nitrate, 0% to about 2%
lithium nitrate, and about 1.5% to about 4% cerium nitrate.
14. The composition according to claim 10, further comprising a
polyhydroxy compound.
15. The composition according to claim 14, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
16. The composition according to claim 15, wherein the composition
comprises about 3% to about 26% of the polyhydroxy compound.
17. The composition according to claim 16, wherein the composition
comprises about 5% to about 20% of the polyhydroxy compound.
18. The composition according to claim 17, wherein the composition
comprises about 7% to about 14% of the polyhydroxy compound.
19. A composition for use with an emission control device to
simultaneously remove particulates, hazardous substances, and
SO.sub.x from a flue gas stream, said composition located at a
point upstream of said emission control device and comprising a
salt selected from the group consisting essentially of sodium
nitrate, sodium nitrite, ammonium nitrate, lithium nitrate, barium
nitrate, and mixtures thereof, provided that the composition does
not comprise ammonium nitrate and sodium nitrite at the same time
and further provided that the composition consists of a dry powder
when both sodium nitrite and barium nitrate are present.
20. The composition according to claim 19, wherein the composition
comprises about 5% to about 25% sodium nitrate, 0% to about 25%
sodium nitrite, 0% to about 50% ammonium nitrate, 0% to about 10%
lithium nitrate, and 0% to about 10% barium nitrate.
21. The composition according to claim 20, wherein the composition
comprises about 8% to about 20% sodium nitrate, 0% to about 20%
sodium nitrite, 0% to about 44% ammonium nitrate, 0% to about 6%
lithium nitrate, and 0% to about 7% barium nitrate.
22. The composition according to claim 21, wherein the composition
comprises about 11% to about 15% sodium nitrate, 0% to about 15%
sodium nitrite, 0% to about 38% ammonium nitrate, 0% to about 2%
lithium nitrate, and 0% to about 4% barium nitrate.
23. The composition according to claim 19, further comprising a
polyhydroxy compound.
24. The composition according to claim 23, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
25. The composition according to claim 24, wherein the composition
comprises about 3% to about 26% of the polyhydroxy compound.
26. The composition according to claim 25, wherein the composition
comprises about 5% to about 20% of the polyhydroxy compound.
27. The composition according to claim 26, wherein the composition
comprises about 7% to about 14% of the polyhydroxy compound.
28. A composition for use with an emission control device to
simultaneously remove particulates, hazardous substances, NO.sub.x,
and SO.sub.x from a flue gas stream, said composition located at a
point upstream of said emission control device and comprising
cerium nitrate and a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, barium nitrate, and mixtures thereof, provided
that the composition does not comprise ammonium nitrate and sodium
nitrite at the same time and further provided that the composition
consists of a dry powder when sodium nitrite is present.
29. The composition according to claim 28, wherein the composition
comprises about 5% to about 25% sodium nitrate, 0% to about 25%
sodium nitrite, 0% to about 50% ammonium nitrate, 0% to about 10%
lithium nitrate, 0% to about 10% barium nitrate, and about 0.5% to
about 10% cerium nitrate.
30. The composition according to claim 29, wherein the composition
comprises about 8% to about 20% sodium nitrate, 0% to about 20%
sodium nitrite, 0% to about 44% ammonium nitrate, 0% to about 6%
lithium nitrate, 0% to about 7% barium nitrate, and about 1% to
about 7% cerium nitrate.
31. The composition according to claim 30, wherein the composition
comprises about 11% to about 15% sodium nitrate, 0% to about 15%
sodium nitrite, 0% to about 38% ammonium nitrate, 0% to about 2%
lithium nitrate, 0% to about 4% barium nitrate, and about 1.5% to
about 4% cerium nitrate.
32. The composition according to claim 28, further comprising a
polyhydroxy compound.
33. The composition according to claim 32, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
34. The composition according to claim 33, wherein the composition
comprises about 3% to about 26% of the polyhydroxy compound.
35. The composition according to claim 34, wherein the composition
comprises about 5% to about 20% of the polyhydroxy compound.
36. The composition according to claim 35, wherein the composition
comprises about 7% to about 14% of the polyhydroxy compound.
37. A method for removing particulates and hazardous substances
from a flue gas stream, comprising adding a composition to the flue
gas stream at a point upstream of an emission control device,
wherein the composition is selected from an aqueous solution and a
dry powder and comprises a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, and mixtures thereof, provided that the
composition does not comprise ammonium nitrate and sodium nitrite
at the same time.
38. A method as set forth in claim 37, wherein the composition
further comprises a polyhydroxy compound.
39. A method as set forth in claim 38, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
40. A method for simultaneously removing particulates, hazardous
substances, and NO.sub.x from a flue gas stream, comprising adding
a composition to the flue gas stream at a point upstream of an
emission control device, wherein the composition is selected from
an aqueous solution and a dry powder and comprises cerium nitrate
and a salt selected from the group consisting essentially of sodium
nitrate, sodium nitrite, ammonium nitrate, lithium nitrate, and
mixtures thereof, provided that the composition does not comprise
ammonium nitrate and sodium nitrite at the same time and further
provided that the composition consists of a dry powder when sodium
nitrite is present.
41. A method as set forth in claim 40, wherein the composition
further comprises a polyhydroxy compound.
42. A method as set forth in claim 41, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
43. A method for simultaneously removing particulates, hazardous
substances, and SO.sub.x from a flue gas stream, comprising adding
a composition to the flue gas stream at a point upstream of an
emission control device, wherein the composition is selected from
an aqueous solution and a dry powder and comprises a salt selected
from the group consisting essentially of sodium nitrate, sodium
nitrite, ammonium nitrate, lithium nitrate, barium nitrate, and
mixtures thereof, provided that the composition does not comprise
ammonium nitrate and sodium nitrite at the same time and further
provided that the composition consists of a dry powder when both
sodium nitrite and barium nitrate are present.
44. A method as set forth in claim 43, wherein the composition
further comprises a polyhydroxy compound.
45. A method as set forth in claim 44, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
46. A method for simultaneously removing particulates, hazardous
substances, NO.sub.x, and SO.sub.x from a flue gas stream,
comprising adding a composition to the flue gas stream at a point
upstream of an emission control device, wherein the composition is
selected from an aqueous solution and a dry powder and comprises
cerium nitrate and a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, barium nitrate, and mixtures thereof, provided
that the composition does not comprise ammonium nitrate and sodium
nitrite at the same time and further provided that the composition
consists of a dry powder when sodium nitrite is present.
47. A method as set forth in claim 46, wherein the composition
further comprises a polyhydroxy compound.
48. A method as set forth in claim 47, wherein the polyhydroxy
compound is selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
49. A method for removing NO.sub.x from a flue gas stream,
comprising adding a composition to the flue gas stream, at a point
upstream of an emission control device, wherein the composition is
selected from an aqueous solution and a dry powder and comprises
cerium nitrate and a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, and mixtures thereof, provided that the
composition does not comprise ammonium nitrate and sodium nitrite
at the same time and further provided that the composition consists
of a dry powder when sodium nitrite is present.
50. A method for removing SO.sub.x from a flue gas stream,
comprising adding a composition to the flue gas stream, at a point
upstream of an emission control device, wherein the composition is
selected from an aqueous solution and a dry powder and comprises a
salt selected from the group consisting essentially of sodium
nitrate, sodium nitrite, ammonium nitrate, lithium nitrate, barium
nitrate, and mixtures thereof, provided that the composition does
not comprise ammonium nitrate and sodium nitrite at the same time
and further provided that the composition consists of a dry powder
when both sodium nitrite and barium nitrate are present.
51. A method for simultaneously removing NO.sub.x and SO.sub.x from
a flue gas stream, comprising adding a composition to the flue gas
stream at a point upstream of an emission control device, wherein
the composition is selected from an aqueous solution and a dry
powder and comprises cerium nitrate and a salt selected from the
group consisting essentially of sodium nitrate, sodium nitrite,
ammonium nitrate, lithium nitrate, barium nitrate, and mixtures
thereof, provided that the composition does not comprise ammonium
nitrate and sodium nitrite at the same time and further provided
that the composition consists of a dry powder when sodium nitrite
is present.
Description
BACKGROUND OF THE INVENTION
This invention relates to emission control for combustion apparatus
burning carbonaceous fuels and, more particularly, to compositions
and methods for the enhanced removal of particulates, hazardous
substances, nitrogen oxides, and sulfur oxides from a flue gas
stream resulting from the combustion of these fuels.
Environmental regulations require that emissions of certain
materials in flue gases be kept at levels not exceeding those set
forth in federal, state, and local specifications. To comply with
these legal mandates, particulate emissions must satisfy certain
standards in terms of pounds per million Btu input, pounds per unit
time, and opacity of stack effluent. The term "particulate" within
the meaning of these restrictions generally refers to fly ash and
other fine particles found in flue gas streams and can include a
host of hazardous substances, such as those listed in 40 CFR .sctn.
302.4 (e.g., arsenic, ammonia, ammonium sulfite, mercury, and the
like).
Acidic gases are also found in flue gas streams. Whenever
sulfur-containing fuels are burned, sulfur is converted to sulfur
dioxide and sulfur trioxide (together known as "SO.sub.x ") and
released into the atmosphere along with other flue gases and
entrained particulate and hazardous substance materials. Combustion
of carbonaceous fuels also results in the formation of nitric oxide
and nitrogen dioxide (together known as "NO.sub.x "), which also
exit the stack with the combustion exhaust materials. However, as
in the case of particulates, the emissions of both NO.sub.x and
SO.sub.x are subject to certain output standards because of acid
rain legislation and mandatory ambient air quality criteria.
Therefore, at least with respect to SO.sub.x, one is required to
burn low-sulfur fuels to ensure compliance with SO.sub.x emission
requirements. This adversely affects older emission control devices
that were originally designed to work in units burning
higher-sulfur fuels. There are also enormous costs associated with
transporting low-sulfur fuels to locations where such fuels are not
found in abundance.
The method of improving particulate control known as flue gas
conditioning is generally understood as adding a chemical into the
flue gas streams of boilers, turbines, incinerators, and furnaces
to improve the performance of downstream emission control devices.
Although the term is usually associated with the removal of
particulates caused by coal combustion, flue gas conditioning can
be equally effective in controlling particulates caused by the
burning of any carbonaceous fuel. As this invention illustrates,
flue gas conditioning can also be used to remove hazardous
substances, NO.sub.x, and SO.sub.x from the flue gas stream.
The performance of downstream emission control devices, such as
electrostatic precipitators, often depends upon the chemistry of
the flue gases and, in particular, such factors as the fuel sulfur
content, particulate composition, particulate resistivity, and the
cohesion properties of entrained particulates, to name a few.
Chemical additives either to the fuel prior to combustion or to the
flue gas stream prior to the electrostatic precipitator can correct
the deficiencies of the precipitator to meet particulate emissions
standards (e.g., mass emission and visual opacity). One of the
objects of flue gas conditioning is to enhance the effectiveness of
the electrostatic precipitation process by manipulating the
chemical properties of the materials found in the flue gas
stream.
Gases, such as ammonia and sulfur trioxide, when injected into the
flue gas stream prior to a cold-side electrostatic precipitator,
have been known to condition the fly ash for better precipitator
performance. Similar results have been obtained with inorganic
chemical compounds, such as ammonium sulfate, sodium bisulfate,
sodium phosphate, or ammonium phosphate. The use of sulfuric acid
has also been proposed, as well as mixtures of these inorganic
compounds in the form of undisclosed "proprietary blends." These
compounds have been added either as a powder or as an aqueous
solution to the flue gas stream.
Organic compounds, such as ethanol amine and ethanol amine
phosphate, have also been used as flue gas conditioning agents.
Free-base amino alcohols, such as morpholine (including morpholine
derivatives), have been used as well to augment the flow
characteristics of treated fly ash. Similarly, the use of
alkylamine (such as tri-n-propylamine) and an acid containing
sulfur trioxide (such as sulfamic acid) has been proposed to lower
the resistivity of fly ash.
Anionic polymers have been employed in situations where the fly ash
resistivity needs to be lowered, particularly when a low-sulfur
coal is utilized. Similarly, cationic polymers have been suggested
whenever the electrical resistivity needs to be raised from a low
value, such as when using high-sulfur coal. Anionic polymers
containing ammonium and sodium nitrate have also been known to
increase the porosity of fly ash for principal application in bag
houses.
The use of inorganic salts, such as sodium sulfate, sodium
carbonate, or sodium bicarbonate added directly to the coal before
combustion has been known to correct the "sodium depletion"
problems of a hot-side precipitator. Sodium carbonate and sodium
bicarbonate have also been injected directly into the flue gas
stream prior to the hot-side precipitator, but this mode of
application has not been commercialized.
The principal post-combustion method for controlling S.sub.x
emissions involves the saturation of basic chemicals with the flue
gases through the use of a "scrubber." In this removal method,
advantage is taken from the fact that SO.sub.x is acidic in nature
and will react with basic additives to form an innocuous sulfate.
Essentially, the principle underlying the various forms of scrubber
technologies is to utilize simple acid-base reactions to control
SO.sub.x emissions. However, conventional scrubber designs are very
capital intensive to build and remain expensive to operate in terms
of labor, energy, and raw material costs.
There are many types of scrubbers currently in use. In wet
scrubbers (which are normally located after the emission control
device), the flue gas is brought into direct contact with a
scrubbing fluid that is composed of water and a basic chemical such
as limestone (calcium carbonate), lime, caustic soda, soda ash, and
magnesium hydroxide/carbonate, or mixtures of these. Water-soluble
nitrite salts have also been added to the scrubbing medium for the
purpose of enhancing the SO.sub.x -removal efficiency of wet
scrubbers. The use of organo phosphonic acid in conjunction with
water-based solutions or slurries that react with sulfur dioxide
have been known to improve the utilization of the basic material in
a wet scrubber. Similarly, polyethylene oxide compounds have been
added to the flue gas as a sludge de-watering agent for improving
the wet scrubber's efficiency.
In dry scrubbers, slurries of lime or mixtures containing lime and
other basic chemicals are injected into the flue gas stream as
sprays. Unlike the wet scrubbers, the injection of these chemicals
in dry scrubbers is usually conducted before the emission control
device. After injection, the unreacted chemicals and reaction
products become entrained with the flue gas stream and are
separated from the flue gas along with other particulates in the
downstream emission control device using common particulate removal
techniques. However, a problem encountered with this method of
SO.sub.x removal is that the unreacted chemicals and reaction
products cause a very heavy particulate load on the downstream
emission control device. This method of removal is also less
efficient than wet scrubbing techniques due to the low reaction
rates between sulfur dioxide and the dry scrubbing additives.
Because of its very high reaction rate with sulfur dioxide, a
compound known as "trona" (a hydrous acid sodium carbonate) has
also been injected into the flue gas stream in dry scrubbers
(upstream from the emission control device) in an effort to reduce
SO.sub.x emissions. Unfortunately, trona produces an undesirable
side effect--it provokes NO.sub.2 formation, which is another
pollutant that is very visible in the plume by its characteristic
brown, aesthetically unacceptable color. Notwithstanding its low
cost, therefore, trona has not acquired much popularity.
The use of soda ash (anhydrous sodium carbonate), caustic soda
(sodium hydroxide), and calcium hydroxide in dry and wet scrubbers
has also proven effective in reducing SO.sub.x emissions. However,
these strong bases have achieved limited commercial success because
of high raw material costs. For example, 1.25 tons of caustic soda
is required for removing every ton of sulfur dioxide produced. For
a 500-megawatt power station burning 2% sulfur coal, it would
require 270 tons of soda per day to keep SO.sub.x emissions within
acceptable levels.
As mentioned previously, NO.sub.x is also produced during the
combustion of carbonaceous fuels. NO.sub.x is generated by several
means, such as the fixation of nitrogen present in combustion
gases, the conversion of fuel-derived nitrogen, and prompt NO.sub.x
formation. Prompt NO.sub.x formation is a small contributor and
only occurs under very fuel-rich operations.
There are several methods by which NO.sub.x emissions have been
controlled. One of these methods include the injection of ammonia
directly into the combustion chamber. Maintaining a close
temperature control between 1650.degree. F. to 1832.degree. F. is
essential under this technique; otherwise, the desired NO.sub.x
removal will not occur, and there will be an excessive emission of
unreacted ammonia. Excessive emissions of unreacted ammonia from
the combustion chamber (known as "ammonia slippage") not only adds
to pollution but also causes pluggage of downstream equipment.
Ammonia slippage thus becomes a problem in its own right.
In another method for NO.sub.x removal, known as "SCR" or selective
catalytic reduction, ammonia is added to the flue gas stream at
temperatures above 800.degree. F. The mixed stream is then passed
over a catalyst where the NO.sub.x removal process is effected.
Despite being the most expensive technology, based both on initial
capital and operating costs, this method has provided the best
removal rates of NO.sub.x (removal rates of 90% to 99% are common).
Unfortunately, however, the catalysts are subject to degradation
over time, as well as poisoning by sulfur-containing gases and
poisoning and blinding by fly ash.
In yet another method, known as "SNCR" or selective non-catalytic
reduction, urea (or its precursors) is injected into the flue gas
stream at temperatures between 1600.degree. F. to 1800.degree. F.
As in the case of the ammonia-injection method for NO.sub.x
control, however, the SNCR process must operate in a narrow
temperature window or else ammonia slippage will occur or too
little NO.sub.x reduction will be achieved. Although combinations
of SNCR and SCR have been proposed, they have presented similar
limitations.
Unlike the aforementioned emission control methods, use of the
compositions of the present invention provides an effective,
efficient, and low-cost means for controlling particulate,
hazardous substance, NO.sub.x, and SO.sub.x emissions without
exhibiting any of the above limitations. Moreover, use of the
invention compositions fills an important need by reducing these
emissions simultaneously. Because of these desirable
characteristics, the present invention constitutes a significant
advancement over prior emission control techniques.
SUMMARY OF THE INVENTION
The present invention provides compositions and methods for flue
gas conditioning to enhance the performance of downstream emission
control devices in removing particulates and hazardous substances
from a flue gas stream, preferably while simultaneously removing
NO.sub.x and SO.sub.x emissions. Although it is preferred that the
invention compositions be added to the flue gas stream at a point
upstream from the emission control device, NO.sub.x and/or SO.sub.x
reduction is still possible without regard to the location at which
these compositions are introduced into the flue gas stream.
The simultaneous removal of particulates and hazardous substances
is accomplished by adding a composition to the flue gas stream that
comprises a salt selected from the group consisting essentially of
sodium nitrate, sodium nitrite, ammonium nitrate, lithium nitrate,
and mixtures thereof, provided that the composition does not
comprise ammonium nitrate and sodium nitrite at the same time. To
simultaneously remove particulates, hazardous substances, and
NO.sub.x, the composition added to the flue gas stream comprises
cerium nitrate and a salt selected from the group consisting
essentially of sodium nitrate, sodium nitrite, ammonium nitrate,
lithium nitrate, and mixtures thereof, provided that the
composition does not comprise ammonium nitrate and sodium nitrite
at the same time and further provided that the composition consists
of a dry powder when sodium nitrite is present. For simultaneously
removing particulates, hazardous substances, and SO.sub.x, the
composition added to the flue gas stream comprises a salt selected
from the group consisting essentially of sodium nitrate, sodium
nitrite, ammonium nitrate, lithium nitrate, barium nitrate, and
mixtures thereof, provided that the composition does not comprise
ammonium nitrate and sodium nitrite at the same time and further
provided that the composition consists of a dry powder when both
sodium nitrite and barium nitrate are present. Finally,
simultaneous particulate, hazardous substance, NO.sub.x, and
SO.sub.x removal is achieved by adding to the flue gas stream a
composition that comprises cerium nitrate and a salt selected from
the group consisting essentially of sodium nitrate, sodium nitrite,
ammonium nitrate, lithium nitrate, barium nitrate, and mixtures
thereof, provided that the composition does not comprise ammonium
nitrate and sodium nitrite at the same time and further provided
that the composition consists of a dry powder when sodium nitrite
is present. For the purpose of obtaining greater yields of
particulate and hazardous substance removal, each of the above
compositions may further comprise a polyhydroxy compound,
preferably selected from the group consisting essentially of
sucrose, fructose, glucose, glycerol, and mixtures thereof.
The introduction of the invention compositions into the flue gas
stream for the purpose of particulate and hazardous substance
removal is primarily intended to enhance the performance of
electrostatic precipitators. However, the compositions of the
invention may also be used to enhance the performance of cyclones,
multi-clones, bag houses, and other emission control devices,
because the compositions are designed to increase the cohesion
properties of the particulates and hazardous substances entrained
in the flue gas stream.
These and other aspects and advantages of the present invention
will become better understood with reference to the following
description, examples, drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graphical illustration reflecting the levels of
SO.sub.x when Formulation I was introduced to a flue gas
stream.
FIG. 2 is a graphical illustration reflecting the levels of
SO.sub.x when Formulation V was introducted to a flue gas
stream.
FIG. 3 is a graphical illustration reflecting the levels of
SO.sub.x when Formulation XI was introduced to a flue gas
stream.
FIG. 4 is a graphical illustration reflecting the levels of
NO.sub.x when Formulation I was introduced to a flue gas
stream.
FIG. 5 is a graphical illustration reflecting the levels of
NO.sub.x when Formulation III was introduced to a flue gas
stream.
FIG. 6 is a graphical illustration reflecting the levels of
NO.sub.x when Formulation V was introduced to a flue gas
stream.
FIG. 7 is a graphical illustration reflecting the levels of
NO.sub.x when Formulation XI was introducted to a flue gas
stream.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the invention comprise one or more of the
nitrates of sodium, ammonium, lithium, barium, and cerium and may
also comprise sodium nitrite. For enhanced removal of particulates
and hazardous substances, the compositions preferably further
comprise a polyhydroxy compound, such as sucrose, fructose,
glucose, glycerol, and mixtures thereof. Depending upon how these
salts and polyhydroxy compounds are combined, their introduction
into the flue gas stream is effective to enhance the performance of
electrostatic precipitators in removing particulates and hazardous
substances while simultaneously reducing either NO.sub.x or
SO.sub.x (or both) from the flue gases.
The invention compositions enhance the performance of electrostatic
precipitators in removing particulates by lowering the electrical
resistivity of entrained particulate materials and by increasing
their cohesivity. Lowering the resistivity improves the initial
collection efficiency of these precipitators, and increasing the
cohesivity promotes the subsequent retention of the collected
particulates. The compositions of the invention lower the high and
low-temperature resistivity of particulates by raising their sodium
and/or lithium levels and by increasing the amount of sulfur
trioxide in the flue gas stream. The invention compositions also
improve the cohesivity of particulates by enhancing their
moisture-absorption capacities and by adding a molten composition
to the particulate-laden flue gas stream. All of these factors
combine to maximize electrostatic precipitator performance. There
may also be other less-understood secondary factors by which the
invention compositions enhance the performance of the electrostatic
precipitator.
The invention compositions also facilitate the removal of hazardous
substances. Hazardous substances often appear in the flue gas
stream as solids or are absorbed or become otherwise attached to
entrained particulates. If the hazardous substances appear in
either of these forms, the downstream electrostatic precipitator
will collect the hazardous substances using the same enhanced
technique for removing particulates outlined above. However, if the
hazardous substances appear in the flue gas stream as a vapor, the
principles underlying their removal are different.
Because vaporous hazardous substances generally have low vapor
pressures, bringing them into contact with a cool surface causes
them to condense to a liquid or solid form. When the invention
compositions are added as atomized aqueous solutions that form
microscopic droplets in the flue gas stream, the water from the
droplets evaporates and the droplets cool for a brief period of
time to a temperature below that of the flue gas stream, thereby
providing the cool surface needed for condensation of the vaporous
hazardous substances. The hazardous substances are thus adsorbed
onto and entrapped by the droplets. Because the invention
compositions have low melting points, the droplets remain in liquid
form in the hot flue gas stream and continue to adsorb and entrap
the condensed hazardous substances until such time as the droplets
are separated from the flue gas stream in the downstream
electrostatic precipitator.
The compositions of the invention also enable the simultaneous
removal of acidic gases, such as NO.sub.x or SO.sub.x, from the
flue gas stream. To simultaneously remove particulates, hazardous
substances, and NO.sub.x, the composition added to the flue gas
stream must at least comprise cerium nitrate. By the same token,
the composition should comprise barium nitrate whenever the
simultaneous removal of particulates, hazardous substances, and
SO.sub.x is desired. However, unlike the requirement for cerium
nitrate in NO.sub.x removal, the presence of barium nitrate is not
absolutely necessary because some degree of SO.sub.x removal will
occur even if that nitrate is omitted from the composition added to
the flue gas stream. Nevertheless, the preferred embodiment is for
the composition to comprise barium nitrate whenever SO.sub.x
removal is sought to be achieved.
To simultaneously remove particulates, hazardous substances,
NO.sub.x, and SO.sub.x the composition added to the flue gas stream
comprises cerium nitrate (for NO.sub.x removal) and should
preferably further comprise barium nitrate (for SO.sub.x removal)
and one or more of the other nitrite and nitrate salts disclosed
herein. The composition may further comprise a polyhydroxy compound
for the purpose of obtaining enhanced particulate and hazardous
substance removal.
Proper dispersion of the invention compositions in the flue gas
stream is important for obtaining effective results. Adequate
dispersion is accomplished by atomizing the composition as it is
being introduced into the flue gas stream. Two-fluid atomization
(where compressed air or steam comprises the fluid other than the
invention composition) is satisfactory, although other methods may
also be used for achieving good atomization. Generally, compressed
air is preferred over steam whenever the invention compositions are
added to the flue gas stream in the form of a dry powder.
There are a number of ways in which the salts and polyhydroxy
compounds disclosed herein may be combined for obtaining enhanced
emission control. Indeed, enhanced emission control will occur even
if one or more of the salts disclosed herein (e.g., sodium nitrate,
sodium nitrite, or ammonium nitrate) are omitted from the
composition that is ultimately added to the flue gas stream.
Nevertheless, the following formulations have been determined by
laboratory and field tests to be the ones most likely to achieve
favorable emission reduction:
Formulation I: NaNO.sub.3, NH.sub.4 NO.sub.3, and LiNO.sub.3.
Formulation II: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3, and a
polyhydroxy compound.
Formulation III: NaNO.sub.3, NH.sub.4 NO.sub.3, and
Ce(NO.sub.3).sub.3.
Formulation IV: NaNO.sub.3, NH.sub.4 NO.sub.3, Ce(NO.sub.3).sub.3,
and a polyhydroxy compound.
Formulation V: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3, and
Ce(NO.sub.3).sub.3.
Formulation VI: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3,
Ce(NO.sub.3).sub.3, and a polyhydroxy compound.
Formulation VII: NaNO.sub.3, NH.sub.4 NO.sub.3, and
Ba(NO.sub.3).sub.2.
Formulation VIII: NaNO.sub.3, NH.sub.4 NO.sub.3,
Ba(NO.sub.3).sub.2, and a polyhydroxy compound.
Formulation IX: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3, and
Ba(NO.sub.3).sub.2.
Formulation X: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3,
Ba(NO.sub.3).sub.2, and a polyhydroxy compound.
Formulation XI: NaNO.sub.3, NH.sub.4 NO.sub.3, Ba(NO.sub.3).sub.2,
and Ce(NO.sub.3).sub.3.
Formulation XII: NaNO.sub.3, NH.sub.4 NO.sub.3, Ba(NO.sub.3).sub.2,
Ce(NO.sub.3).sub.3, and a polyhydroxy compound.
Formulation XIII: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3,
Ba(NO.sub.3).sub.2, and Ce(NO.sub.3).sub.3.
Formulation XIV: NaNO.sub.3, NH.sub.4 NO.sub.3, LiNO.sub.3,
Ba(NO.sub.3).sub.2, Ce(NO.sub.3).sub.3, and a polyhydroxy
compound.
Formulation XV: NaNO.sub.3, NaNO.sub.2, and LiNO.sub.3.
Formulation XVI: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3, and a
polyhydroxy compound.
Formulation XVII: NaNO.sub.3, NaNO.sub.2, and Ce(NO.sub.3).sub.3
(dry powder).
Formulation XVIII: NaNO.sub.3, NaNO.sub.2, Ce(NO.sub.3).sub.3, and
a polyhydroxy compound (dry powder).
Formulation XIX: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3, and
Ce(NO.sub.3).sub.3 (dry powder).
Formulation XX: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3,
Ce(NO.sub.3).sub.3, and a polyhydroxy compound (dry powder).
Formulation XXI: NaNO.sub.3, NaNO.sub.2, and Ba(NO.sub.3).sub.2
(dry powder).
Formulation XXII: NaNO.sub.3, NaNO.sub.2, Ba(NO.sub.3).sub.2, and a
polyhydroxy compound (dry powder).
Formulation XXIII: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3, and
Ba(NO.sub.3).sub.2 (dry powder).
Formulation XXIV: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3,
Ba(NO.sub.3).sub.2, and a polyhydroxy compound (dry powder).
Formulation XXV: NaNO.sub.3, NaNO.sub.2, Ba(NO.sub.3).sub.2, and
Ce(NO.sub.3).sub.3 (dry powder).
Formulation XXVI: NaNO.sub.3, NaNO.sub.2, Ba(NO.sub.3).sub.2,
Ce(NO.sub.3).sub.3, and a polyhydroxy compound (dry powder).
Formulation XXVII: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3,
Ba(NO.sub.3).sub.2, and Ce(NO.sub.3).sub.3 (dry powder).
Formulation XXVIII: NaNO.sub.3, NaNO.sub.2, LiNO.sub.3,
Ba(NO.sub.3).sub.2, Ce(NO.sub.3).sub.3, and a polyhydroxy compound
(dry powder).
The concentration of sodium nitrate (NaNO.sub.3) in the above
formulations is about 5% to about 25%, preferably about 8% to about
20%, more preferably about 11% to about 15%, and especially about
13%. Whenever sodium nitrite (NaNO.sub.2) is present in these
formulations, it is in a concentration of about 5% to about 25%,
preferably about 8% to about 20%, more preferably about 11% to
about 15%, and especially about 13%. Whenever ammonium nitrate
(NH.sub.4 NO.sub.3) is present, it is in a concentration of about
10% to about 50%, preferably about 20% to about 44%, more
preferably about 30% to about 38%, and especially about 34%.
Whenever lithium nitrate (LiNO.sub.3) is present, it is in a
concentration of about 0.4% to about 10%, preferably about 0.6% to
about 6%, more preferably about 0.8% to about 2%, and especially
about 1%. Whenever cerium nitrate (Ce(NO.sub.3).sub.3) and/or
barium nitrate (Ba(NO.sub.3).sub.2) are present, each are found in
a concentration of about 0.5% to about 10%, preferably about 1% to
about 7%, more preferably about 1.5% to about 4%, and especially
about 2.5%. Finally, whenever the polyhydroxy compound is present,
it is in a concentration of about 3% to about 26%, preferably about
5% to about 20%, more preferably about 7% to about 14%, and
especially about 10%. The remainder of the composition is either
water or a dry filler depending, respectively, on whether the
composition is applied as an aqueous solution or as a dry powder.
The dry filler may comprise any inert material, such as clay,
diatomite, silica, alumina, and the like.
Formulations I through XVI may be added to the flue gas stream
either in the form of a finely divided dry powder or as an aqueous
solution. Preferably, these formulations are added in the form of
an aqueous solution in order to provide for the removal of vaporous
hazardous substances and for obtaining greater particulate
cohesivity. However, because sodium nitrite cannot coexist with the
nitrates of cerium and barium in an aqueous solution, Formulations
XVII through XXVIII must consist of a dry powder. Similarly,
because sodium nitrite cannot coexist with ammonium nitrate in an
aqueous solution and because the combination of sodium nitrite and
ammonium nitrate is unstable under the temperatures prevailing in
the flue gas stream, Formulations XV through XXVIII do not comprise
ammonium nitrate.
All of the above formulations have been determined by laboratory
tests to be suitable for removing particulates and hazardous
substances. Formulations III through VI and Formulations XVII
through XX are capable of simultaneously removing particulates,
hazardous substances, and NO.sub.x, but Formulation VI is the
preferred composition for this purpose. Formulations VII through X
and Formulations XXI through XXIV are capable of simultaneously
removing particulates, hazardous substances, and SO.sub.x, although
the composition preferred for this purpose is Formulation X.
Formulations XI through XIV and Formulations XXV through XXVIII are
capable of simultaneously removing particulates, hazardous
substances, NO.sub.x, and SO.sub.x ; however, the preferred
composition for this purpose is Formulation XIV. It should be
observed that Formulations XVII through XXVIII are less effective
in removing vaporous hazardous substances because of their
application as a dry powder to the flue gas stream.
Selection of a preferred formulation depends upon economic factors
and whether enhanced NO.sub.x and SO.sub.x reduction is needed. For
example, units burning low-sulfur coal may not require a
formulation that is aimed at SO.sub.x reduction (e.g., Formulations
VII through XIV and Formulations XXI through XXVIII). If neither
NO.sub.x nor SO.sub.x reduction is required, one might consider
sparing the expense of adding barium and cerium nitrates by using
either Formulations I, II, XV, or XVI. Among these four
formulations, Formulations I and II are primarily designed for use
in cold-side precipitators, and Formulations XV and XVI are
primarily designed for use in hot-side precipitators. With respect
to Formulations I and II, Formulation II is preferred over
Formulation I during cold-side precipitator operations because
greater yields of particulate and hazardous substance removal is
obtained with the addition of the polyhydroxy compound. Similarly,
with respect to Formulations XV and XVI, Formulation XVI is
generally preferred over Formulation XV in hot-side precipitator
operations, particularly when the formulation is applied during
periods within which the hot-side precipitator is coming on-line
and off-line so as to cause the hot-side precipitator to operate in
a mode somewhere between that of a hot-side and a cold-side
precipitator.
Because these formulations are designed to work in conjunction with
an emission control device, they are added to the flue gas stream
preferably at a point upstream from the device in order to allow
enhanced particulate and hazardous substance removal to occur.
However, NO.sub.x and SO.sub.x reduction is still possible without
regard to the location at which the formulations are introduced
into the flue gas stream. For example, if the formulations for
NO.sub.X and SO.sub.X removal (e.g., Formulations XI through XIV
and Formulations XXV through XXVIII) are added to the flue gas
stream at a point downstream from the emission control device,
NO.sub.X and SO.sub.x reduction will still occur, but the
concomitant benefit of particulate and hazardous substance
reduction may not be obtained.
For the formulations to be effective, the temperature of the flue
gas stream should be between 200.degree. F. to 1800.degree. F. The
temperatures found in both cold-side electrostatic precipitators
(which normally operate with temperatures between 250.degree. F. to
450.degree. F.) and hot-side electrostatic precipitators (which
normally operate with temperatures between 600.degree. F. to
800.degree. F.) fall within the above effective temperature range.
Additionally, if the aqueous form of the formulation comprises
either cerium nitrate or barium nitrate, the pH level should be
adjusted to a level below 2.5 to avoid cerium and/or barium
precipitation.
In situations when SO.sub.x emission control is desired and the
levels of calcium and magnesium as oxides comprise less than 5% of
the other inorganic compounds present in the particulate, it is
advantageous to increase the levels of calcium and magnesium by
adding a compound containing the deficient alkaline material, such
as limestone, dolomite, magnesite, lime, slaked lime, magnesium
oxide, and the like, to the fuel prior to its combustion or to the
flue gas stream at a point upstream from the location where the
introduction of the SO.sub.x -removal formulation will occur.
Similarly, whenever a SO.sub.x -removal formulation in dry form is
applied and a low-ash fuel is burned in which the fly ash content
of the fuel is less than 5%--such as in the case of oil or gaseous
fuels (e.g., natural gas, cokeoven gas, refinery gas, or blast
furnace gas)--these alkaline materials can be incorporated directly
into the SO.sub.x -removal formulation (e.g., Formulations XXI
through XXVIII). The amount of alkaline materials to be added will
naturally depend upon the amount of SO.sub.x removal desired;
higher amounts of SO.sub.x removal will require greater amounts of
alkaline materials.
The proper formulation dosage for treating the flue gas stream is
best defined in terms of the Btu heat input level of the fuel being
burned. Specifically, the formulations are applied with a dosage
ranging between about 1.5 g to about 150 g per million Btu input,
preferably between about 3 g to about 30 g per million Btu input,
more preferably between about 5 g to about 30 g per million Btu
input, and especially about 8 g per million Btu input. However,
variations in these dosages may occur as defined by the user and
the conditions prevailing in the flue gas stream (e.g., humidity,
entrained particulate levels, etc.).
EXAMPLES
The following examples further demonstrate the instant invention.
These examples should not, however, be construed as limiting the
instant invention in any way.
Example 1
To test the effectiveness of the disclosed formulations for
controlling particulates, laboratory tests were conducted that
measured the sodium and ammonia levels of treated and untreated fly
ash obtained from a coal-fired utility plant. A 100 g sample of fly
ash from a utility plant was mixed with an aqueous solution
containing 42 g of water and 0.3 g of Formulation I (consisting of
13% NaNO.sub.3, 36% NH.sub.4 NO.sub.3, and 1% LiNO.sub.3). The
paste-like sample was mixed with a spatula to ensure uniform and
thorough mixing. A blank for comparison consisting of only the fly
ash and water was also prepared in the same manner. Both samples
were then dried overnight in an oven maintained at 220.degree. F.
(.+-.10.degree. F.). Thereafter, the samples were crushed and
ground to a fine powder. A two-gram portion of each of the ground
samples was then mixed separately with 200 g of distilled water and
shaken thoroughly. The samples were filtered and the supernatants
analyzed to determine the levels of sodium and ammonia. The results
of these laboratory tests are reported in TABLE I.
TABLE I ______________________________________ Analysis of
Untreated Fly Ash and Fly Ash Treated with Formulation I System
Sodium Ammonia ______________________________________ Untreated Ash
220 ppm <50 ppm Treated Ash 545 ppm <50 ppm
______________________________________
As illustrated in TABLE I, the level of supernatant sodium doubled
when the fly ash was treated with Formulation I, indicating the
addition of sodium to the fly ash, while the level of supernatant
ammonia remained largely unchanged. By increasing the level of
sodium (derived from sodium nitrate) without obtaining a
corresponding increase in the level of ammonia (derived from
ammonium nitrate), the tests reveal that Formulation I is effective
in lowering the resistivity of fly ash (thus providing improved
electrostatic precipitator performance) without producing
undesirable ammonia residue in the fly ash.
Example 2
Laboratory tests were also conducted to study the thermal
properties (and physical state) of various nitrate and nitrite salt
combinations. To perform this study, formulations containing
nitrite and nitrate salt combinations were diluted in distilled
water. The mixture ratios by weight of nitrite and nitrate salts in
the formulations are delineated in TABLE II. For example, 5 g of
technical grade sodium nitrate (Chilean Nitrate Corporation,
Norfolk, Va.) and 5 g of technical grade lithium nitrate (Cyprus
Foote Mineral Company, Kings Mountain, N.C.) was dissolved in 20 g
of distilled water to prepare a mixture of 1:1 by weight sodium
nitrate and lithium nitrate.
A 5 g to 10 g sample of each aqueous solution was placed in a
pre-weighed porcelain crucible and dried overnight at 230.degree.
F. (.+-.10.degree. F.). The samples were then cooled in a
desiccator and the weight recorded after cooling. The samples were
again placed in an oven maintained at specified temperatures (see
TABLE II), and after two hours, their physical state was noted.
Thereafter, the samples were re-cooled and re-weighed to determine
the weight loss after the second heating. The results from these
tests are reported in TABLE II.
TABLE II
__________________________________________________________________________
Thermal Properties of Some Formulated Mixtures 270.degree. F./% wt
300.degree. F./% wt 350.degree. F./% 420.degree. F./% wt %
Component lossloss loss
__________________________________________________________________________
1:1 by wt. NaNO.sub.3 /LiNO.sub.3 solid/none solid/none semi
molten/1.7 solid/0.7 4:1 by wt. NaNO.sub.3 /LiNO.sub.3 solid/none
solid/none semi molten/0.5 solid/0.6 5:1 by wt. NaNO.sub.3
/Ce(NO.sub.3).sub.3 solid/none solid/none solid/3.2 semi solid/6.0
4.5:4.5:1 by wt. NaNO.sub.3 /NH.sub.4 NO.sub.3 /Ce(NO.sub.3).sub.3
molten/none molten/.dagger. solid/5.0 molten/15.8 25:65:5:5 by wt.
NaNO.sub.3 /NH.sub.4 NO.sub.3 /Ce(NO.sub.3).sub.3
/Ba(NO.sub.3).sub.2 semi molten/.dagger. molten/.dagger. molten/3.1
molten/.dagger. 6:3:1 by wt. NaNO.sub.3 /NaNO.sub.2 /LiNO.sub.3
solid/none solid/none solid/none molten/none
__________________________________________________________________________
.dagger.Percentage weight loss not available
As shown in TABLE II, the stated combinations of sodium nitrate,
sodium nitrite, ammonium nitrate, lithium nitrate, cerium nitrate,
and barium nitrate are stable at temperatures well above
270.degree. F. and remain as a liquid. Depending upon the
temperature of the flue gas stream during a particular application,
a selection of an appropriate formulation may be made by the user
to achieve optimal emission control.
Example 3
Further laboratory tests were performed to determine the moisture
absorption capacities of combinations of sodium nitrate, ammonium
nitrate, lithium nitrate, and cerium nitrate at various humidities.
An aqueous solution of a given composition (see TABLE III) was
weighed in a pre-weighed porcelain crucible and then dried
overnight at 230.degree. F. (.+-.10.degree. F.). After the dried
composition was cooled, it was weighed quickly to avoid moisture
absorption from the atmosphere and placed in a glass desiccator
containing about 12% to about 18% sulfuric acid solution in
distilled water. It is known that a 11.02% solution of sulfuric
acid in a closed container maintains a humidity of 95% and that a
solution of 17.91% sulfuric acid maintains a humidity of 90% at
70.degree. F. The crucibles were left in the desiccator until the
weight changes between successive weight measures became
negligible. This process required approximately 50 to 100 hours of
equilibration depending upon the composition being tested. The
moisture absorption percentages measured during these tests are
reported in TABLE III.
TABLE III
__________________________________________________________________________
Moisture Absorption Studies* Composition NH.sub.4 NO.sub.3
LiNO.sub.3 1:1 - LiNO.sub.3 /Ce(NO.sub.3).sub.3 6:4 - NH.sub.4
NO.sub.3 /Ce(NO.sub.3).sub.3 4:4:1 - NaNO.sub.3 /NH.sub.4 NO.sub.3
/LiNO.sub.3 4:1 - NH.sub.4 NO.sub.3 /LiNO.sub.3
__________________________________________________________________________
Moisture 3.7 80 81.3 7.7 22.97 42.3 absorption %
__________________________________________________________________________
*Moisture absorption at 70.degree. F. @ 90-95% RH
As illustrated in TABLE III, the stated combinations of sodium
nitrate, ammonium nitrate, lithium nitrate, and cerium nitrate
resulted in varying moisture absorption percentages, depending upon
how these nitrates were combined. Although one would expect the
moisture absorption capacity of a composition comprising 100%
lithium nitrate to be higher when compared to a composition
comprising only 50% lithium nitrate (e.g., 1:1 LiNO.sub.3
/Ce(NO.sub.3).sub.3), the moisture absorption capacity largely
remained the same. This result indicates that there is a
synergistic effect in the combination of lithium nitrate and the
other nitrates that were tested.
Example 4
Finally, laboratory data was obtained on the cohesion properties of
plant fly ash with various formulations. For this purpose, fly ash
obtained from a plant was treated with the formulations illustrated
in TABLE IV.
TABLE IV
__________________________________________________________________________
Formulations (in H.sub.2 O) for Particulate, Hazardous Substances,
NO.sub.x, and SO.sub.x Removal Formulation % NaNO.sub.3 % NH.sub.4
NO.sub.3 % LiNO.sub.3 % Ba(NO.sub.3).sub.2 % Ce(NO.sub.3).sub.3 %
NO.sub.3 % Sucrose pH
__________________________________________________________________________
I 13 36 1 0 0 38.6 0 6 II 106 6 III 0 1.5 XI 0 1.5 XIII 0 1.5
__________________________________________________________________________
0.5 g, 1 g, and 5 g of the above formulations were each diluted
with about 40 g water and then mixed separately with 100 g of fly
ash. A blank for comparison was prepared by mixing 100g of fly ash
with about 40 g of water. Additional samples (Samples A, B, and C
as reflected in TABLE V) were prepared in the same manner used for
preparing the above formulations. All of these fly ash mixtures
were of a paste consistency. The mixtures were then dried overnight
at 220.degree. F. After drying, the mixtures were crushed to a
powder.
Each of the fly ash mixtures were then rolled in a pan at room
temperature for 5 minutes. Rolling produced "balling" of various
sizes in the rolled fly ash mixtures. The number and size of the
balls indicated the agglomeration or inducement of cohesion by the
formulation. A system of rating on a visual scale of 0 (no
agglomeration) to 10 (maximum agglomeration) for agglomeration
occurring in more than one half of the tested fly ash mixture was
used to judge the formulations' effectiveness. As illustrated in
TABLE V, all of the above formulations produced significant levels
of agglomeration over no treatment; the formulations also produced
more agglomeration than Samples A, B, and C (compositions noted in
TABLE V) that were tested for comparison.
TABLE V ______________________________________ Agglomeration Level
of Fly Ash with Various Treatments Agglomeration
______________________________________ Treatment Description Level
______________________________________ Fly Ash (without treatment)
<0.5 Fly Ash with Sample A (20% NaNO.sub.3 & 80% H.sub.2 O)
.about.1 Fly Ash with Sample B (50% NH.sub.4 NO.sub.3 & 50%
H.sub.2 O) .about.3 Fly Ash with Sample C .about.5 (25% NaNO.sub.3
& 25% NH.sub.4 NO.sub.3 & 50% H.sub.2 O) Fly Ash with
Formulation I .about.7 Fly Ash with Formulation II .about.8 Fly Ash
with Formulation III .about.8 Fly Ash with Formulation XI .about.8
Fly Ash with Formulation XIII .about.6
______________________________________
The laboratory test results described above in EXAMPLES 1 through 4
indicate that the formulations disclosed herein are effective in
lowering the resistivity of particulates by increasing particulate
sodium levels, they are stable at temperatures well above
270.degree. F. and remain as a liquid, and they improve particulate
cohesivity by enhancing both the moisture-absorption capacities and
agglomeration properties of particulates.
Example 5
A series of field tests were also conducted to test the
effectiveness of the formulations in removing particulates,
NO.sub.x, and SO.sub.x with favorable results. The field tests were
conducted with Formulations I, III, V, and XI on a 350-megawatt
power generating unit in the midwestern United States.
The tests performed with selected formulations were conducted by
first diluting the formulations with plant well water in the ratio
by volume of 1 part product with 5 to 10 parts of water. Each
diluted formulation was then injected in atomized form into four
gas ducts upstream from the electrostatic precipitator (only one
formulation was used per test) at a combined dosage rate of 6.3 g
to 28 g per million Btu input. Adequate atomization was achieved by
injecting the formulations through a set of eight, internally mixed
dual-fluid nozzles (two nozzles per duct), wherein compressed air
was used as the atomizing fluid. The nozzles used in these tests
are well known in the art and are available from either Spraying
Systems of Wheaton, Ill. or Bete Fog Jet of Greenfield, Mass.,
among others. Although compressed air was used to atomize the
diluted product in this instance, steam could have been used
equally well.
Fly ash samples during each test were collected for analysis and
their quality examined with respect to their acceptability as
"cement aggregate." The breakdown of components from a typical
untreated fly ash sample obtained from the test site is reported in
TABLE VI (the range of high and low values for each component
covered a spread of .+-.10%).
TABLE VI
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Analysis of the Fly Ash (Before Treatment) % Al.sub.2 O.sub.3 %
Fe.sub.2 O.sub.3 % SiO.sub.2 % CaO % MgO % SO.sub.3 % Na.sub.2 O %
K.sub.2 O % Moist. % LOI*
__________________________________________________________________________
20.5 5.5 42.8 23.4 4.6 1.5 1.2 0.3 0.1 0.3
__________________________________________________________________________
*LOI = Loss on ignition
The typical properties (with high and low values) of the coal used
in these tests are provided in TABLE VII.
TABLE VII ______________________________________ Analysis of Coal
Coal Parameter Analysis (Hi/Lo)
______________________________________ % Moisture 27 (27.8/26.5) %
Fly Ash 5.2 (6.5/4.4) % Sulfur 0.25 (0.37/0.22) % Na.sub.2 O 1.3
(1.6/0.99) Btu/lb. 8700 (8900/8600)
______________________________________
Several parameters were monitored. They included metered opacities
(instantaneous and six-minute averages), electrostatic precipitator
power levels, NO.sub.x and SO.sub.x data from the Continuous
Emission Analyzer, flue gas temperatures, power generation
(megawatts), and data on the coal being burned (quantity and
quality). A comparison was also made of the results obtained with a
commercial additive that the plant had been using for several years
for particulate control.
The chemical and physical analyses of the fly ash samples treated
with Formulations I, V, and XI, together with the ASTM test results
(ASTM C618) on the acceptability as "cement aggregate" of each
sample, are reported respectively in TABLES VIII through X.
TABLE VIII
__________________________________________________________________________
Chemical Analysis of Fly Ash (With Treatment) ASTM C618 Parameter
Formulation Ication Formulation V Formulation XI
__________________________________________________________________________
% Aluminum Oxide 19.43 19.83 20.01 % Iron Oxide 5.18 5.25 % Silica
42.32 39.63 % Sum of AL, FE, and SI Oxides 50 Min. 64.89 % Calcium
Oxide 25.01 % Magnesium Oxide 4.95 % Sulfur Trioxide 1.62 %
Available Alkali 1.20 % Availabie Sodium Oxide 1.00 % Available
Potassium Oxide 0.29
__________________________________________________________________________
TABLE IX
__________________________________________________________________________
Physical Analysis of Fly Ash (With Treatment) ASTM C618 Parameter
Formulation Iification Formulation V Formulation XI
__________________________________________________________________________
Percentage retaincd on 325 Sieve 34.0 Max. 16.28 18.26 25.55
Percentage moisture in ash Max. 3.0 0.02 0.02 Percentage lost on
ignition Max. 6.0 0.33 0.37 H.sub.2 O requirement (% control) 105
Max. 102.50 102.50 Autoclave expansion Max. 0.8 0.012 0.031
Specific gravity 2.59 2.56
__________________________________________________________________________
TABLE X
__________________________________________________________________________
Pozzolanic Activity Index for Fly Ash (With Treatment) ASTM C618
Parameter Formulation Iification Formulation V Formulation XI
__________________________________________________________________________
Percentage of cement control 75 Min. 111.26 101.21 87.51 PSI of
cement control 4138 4138 PSI of Sample 4604 3621
__________________________________________________________________________
From TABLES VIII through X, it is evident that the treated fly ash
samples met all of the criteria set by ASTM in its test method C618
and had acceptable "cement aggregate" qualities.
The field-tested formulations were determined to significantly
improve the performance of the electrostatic precipitator based on
the observed decrease in opacity levels in the flue gas stream.
Lowered particulate resistivity was evident from the increased
levels of primary and secondary currents in the precipitator and
decreased levels of sparking. Increased particulate cohesivity was
evidenced by lowered opacity spikes, which are generally
attributable to the reintroduction of collected particulates into
the flue gas stream whenever the collecting plates are cleaned by
mechanical vibration or rapping. Moreover, the data obtained from
the Continuous Emission Analyzer demonstrated that the formulations
were also effective in reducing NO.sub.x and SO.sub.x emissions as
is graphically illustrated in FIGS. 1 through 7.
Although the present invention has been described in considerable
detail with reference to certain preferred versions thereof, other
versions are possible. The above description is for the purpose of
teaching the person of ordinary skill in the art how to practice
the present invention, and it is not intended to detail all obvious
modifications and variations that will become apparent to the
skilled worker upon reading the description. It is intended,
however, that all such obvious modifications and variations be
included within the scope of the present invention which is defined
by the following claims. Accordingly, the spirit and scope of the
appended claims should not be limited to the description of the
preferred versions contained herein.
* * * * *